This invention relates to position determination systems, in particular an apparatus for indicating direction and heading. Specifically, the present invention pertains to a method for using such an apparatus to generate and maintain an up-to-date database of object locations and characteristics.
Satellite positioning system (SATPOS) devices that determine position using the satellites of the US Global Positioning System (GPS) are commonly used for navigation of vessels, vehicles, airplanes, and other conveyances. SATPOS devices are also used for surveying, construction site planning and management, mining, oil and gas exploration and development, etc. Also, handheld SATPOS devices are used for personal navigation, data collection, data maintenance, etc.
SATPOS devices are quite effective for indicating the position of the SATPOS device. Position is typically indicated using either an alphanumeric indication of position or by displaying a map that indicates position. Alphanumeric indications of position typically include coordinates such as, for example, latitude and longitude, World Geodetic Survey (WGS) coordinates, etc.
Map displays typically indicate position by an icon or other indicator visible on a map. One such map display, typically referred to as a moving map display, displays the position of the SATPOS in the center of the displayed map. Such map displays typically are oriented such that the top of the SATPOS device""s display indicates North (either magnetic North or true North). That is, irrespective of the direction in which the SATPOS device is actually oriented, North is shown at the top of the display. For users that intuitively know which direction is North, such maps are adequate for locating features displayed on the map. However, for users that do not know where North is, or when visibility is obscured such that the user cannot determine where North is, such maps are inadequate for guiding the user to a destination or feature on the map.
For many commercial applications of SATPOS systems, such as construction site planning and management, surveying, navigation, etc., it is essential that an operator be able to locate features displayed on the map. Such users typically operate a separate device for indicating direction such as a conventional magnetic compass.
Some SATPOS devices indicate the direction of movement of the SATPOS device, typically referred to as xe2x80x9cheading.xe2x80x9d Typically, heading is determined by analysis of determined position in relation to prior determinations of position as the SATPOS moves. Typically, SATPOS devices that indicate heading use a map display oriented such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to North (either magnetic North or true North).
Some prior art SATPOS devices orient the displayed map such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to the direction of movement calculated by the SATPOS device. This gives a good approximation of the user""s heading as long as the user continues to move and as long as the SATPOS unit is oriented in the direction of movement, allowing a user to easily determine the location of features visible on the display.
However, when the SATPOS device stops moving, determination of heading can no longer be made. Some SATPOS systems maintain the previous heading for orienting the moving map display for a given time interval. Other prior art SATPOS systems default to positioning North at the top of the map. This can be quite confusing to the user.
Recently, digital compasses have been developed that can indicate direction. However, digital compasses must be calibrated to properly align the digital compass prior to use. Also, each time that magnetic environment around the compass changes, the digital compass must be recalibrated. Digital compasses are typically calibrated by moving the digital compass in a full horizontal arc. The calibration process takes time and is prone to operator error. Also, calibration error can occur as a result local magnetic anomalies.
What is needed is a method and apparatus for providing an accurate indication of heading to a user of a SATPOS device. Also, a method and apparatus are needed that meet the above need and that accurately indicate direction when the SATPOS is not moving. Also, a method and apparatus are needed that are easy to use and that do not require a user to manually calibrate a compass.
As described above, a SATPOS device can be used for surveying, construction site planning and management, mining, oil and gas exploration and development, etc. A problem occurs when a user arrives at a particular site and attempts to acquire positioning determining signals such as signals from GPS satellites. At any one location, four GPS satellites are typically xe2x80x9cin viewxe2x80x9d (that is, they are in a position such that they could be used for acquiring a positioning determining signal). In general, signals from at least three satellites are needed to accurately determine position, direction and/or heading. However, at some sites, the SATPOS cannot acquire a signal from one or more of the satellites because the signal is obstructed by features present at the site. For example, at a downtown site, signals may be blocked at certain times of day by surrounding buildings. As the satellites move in their orbit, they may come into view of the site at a later time.
Thus, during certain periods of the day, a user may not be able to acquire a signal from a number of satellites sufficient for accurately determining position, direction and/or heading. If, instead, the user had arrived at the site at a different time, he or she would have been able to receive a signal from a sufficient number of satellites.
As a result, a user""s time can be wasted because of having to make repeated visits to a particular location, or from having to wait at the site for a period of time, until enough satellites can be viewed so that accurate positioning information can be obtained. This problem is exacerbated for SATPOS applications in which a large number of sites have to be visited on a regular basis.
Accordingly, what is also needed is a method and/or system that can be used to identify when a sufficient number of satellites can be viewed at a particular location, so that positioning information (including direction and heading) can be accurately determined. Furthermore, what is needed is a method and/or system that can satisfy the above need and that is convenient to implement. The present invention meets this need and the above needs.
The present invention provides a method and apparatus that accurately indicate direction and heading to a user of a satellite positioning system (SATPOS) device. The present invention also provides a method and system for identifying when a sufficient number of satellites can be viewed at locations of interest so that positioning information can be accurately determined at each location. In addition, the present invention provides a method and system that are conveniently implemented.
An integrated position and direction system is disclosed that includes a SATPOS having a receiver adapted to receive satellite position determining signals. The integrated position and direction system of the present invention also includes a digital compass that is adapted to determine direction.
The integrated position and direction system also includes a controller for controlling the operations of the integrated position and direction system. The controller is coupled to the SATPOS, the digital compass, and to a display.
In one embodiment of the present invention, when the SATPOS is moving, the direction of movement or xe2x80x9cheadingxe2x80x9d determined by the SATPOS is indicated on the display. When the SATPOS is not moving, the direction given by the digital compass is indicated on the display. Therefore, while the SATPOS is moving, the heading is indicated, and when the SATPOS is not moving, direction is indicated using the digital compass. Thus, the present invention provides a method and apparatus for providing an accurate indication of both heading and direction to a user of a SATPOS device.
In one embodiment, the digital compass is automatically calibrated by the SATPOS when the SATPOS is moving. This calibration can be initiated by the user or can be fully automatic. More particularly, the digital compass of the present invention is calibrated automatically, either as a result of user input (e.g., selection of an icon, pressing of a button, etc.), or as a result of user-defined criteria for automatic calibration. That is, the user can program the present invention to automatically calibrate the digital compass (e.g., when velocity exceeds a given threshold, whenever the SATPOS begins moving, periodically while the SATPOS is moving, when the difference between the SATPOS determined heading differs from the heading indicated by the digital compass by more than a predetermined threshold, etc.). Thus, the position and direction system of the present invention is easy to use because there in no need for a user to calibrate a compass as is required using a prior art compass alone.
In another embodiment, a method and system for generating and maintaining a database comprising a location-sensitive timetable are disclosed. At multiple locations, a receiving device (e.g., the SATPOS) listens for broadcast signals from broadcasting devices (e.g., satellites). For each location, the SATPOS records the time and date and the number of satellites from which a signal is received. The SATPOS can also record the identities of satellites that can and cannot be picked up. The information recorded by the SATPOS can be used to automatically generate a timetable showing the dates and times of day for each location that are and are not satisfactory for obtaining and maintaining positioning information, based on the number of satellites available for viewing. The recorded information can also be used to automatically predict future dates and times for each location that will or will not be satisfactory for obtaining and maintaining positioning information. Each visit to a location accumulates additional information regarding when satellites will and will not be available for viewing. In this manner, the timetable is automatically generated and updated. The timetable can be used as the basis for a schedule for visiting each location when satellite viewing will be satisfactory. In this manner, the timetable can be automatically factored into mission planning for data maintenance.
In an alternate embodiment, the position and characteristics (e.g., height, width, etc.) of the features (e.g., buildings, trees, canyons, and other such objects that might block a broadcast signal) at each location are recorded. This information is used along with satellite constellation information (e.g., issue of data ephemeris information) to predict the dates and times when satellites will be blocked from view of a SATPOS device. From this information, the timetable can then be generated and used as the basis for a schedule for mission planning.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the various drawing figures.